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Re: blew my head gasket running 15 psi boost

Ask a hundred guys and you will probably get 100 answers. This is just my opinion, but here goes.

First, insure both block and head are dead on true. Some folks don't thing BMW blocks get distorted, but they do, although not by much. The heads are usually a little off, especially if it ever got hot.

Second, I think the factory head gasket is sufficient to run 10 psi without further mods, assuming both block and head are true.

Third, if you are wanting to run 15 psi sustained, I think the best all around combo is the factory gasket with a stainless "O" ring in the head. Assuming your block is dead on, I would disassemble the head, take it with the new head gasket to a good machine shop for a scim cut and an "O" ring job.

I am sure others will tell you copper is the way to go. I have a copper head gasket on my 745i right now. It took two tries to get it to seal the water leaks, and even then, after a few thousand miles, I had a slight seepage. Ended up puting stop leak in to insure no seepage. Also, with copper, to do it right, you will need both the block and head skim cut, have the block machined for "O" rings, and have the head machined for receiver grooves. If you want to be able to do this job without pulling the whole engine, go with an "O" ringed head and the factory gasket.

I would also use the factory head bolts. Although they are not "single use" items, you can buy new ones for a little extra peace of mind. They are not expensive. Others will advise you use studs, but one of the guys on the 745i board had a bad experience with brand "A" sutd kit. Didn't even get over the factory 6 psi boost and the head gasket was pushed out on one side. Check out his post:

Re: blew my head gasket running 15 psi boost

I would definalely run head studs. Head bolts aren't meant for the pressures of a turbo. Any turbo car thats running a good amount of power will probably have studs. You can use a stock material gasket for 12psi also.

I used ARP studs. The directions say >>>

simply; using their moly grease, torque to 80lb/ft, using 30 weight oil, torque to 120lb/ft.
I used the moly grease but had some residual oil in the holes so after exhaustive calculating.... I said "screw it" and torqued to 100lb/ft... 40, 60, 80, 100.

We've been running 18psi on the TCD 535 >>>

what about the 12.9 grade hex head bolt from my 88

I had an 88 325i m20 motor that had metric 12.9 grade head bolts. ARP claim that there bolts are 15% stronger than imperical grade 8 bolts. After some calculations I found out that the 12.9 should be stronger than the ARP... All this to ask one question: Where can I find these 12.9 hex head bolts? I need new ones and the dealer only carries 10.9 torx head bolts.

Try some industrial supply houses like Grainger.

Re: blew my head gasket running 15 psi boost

I would say o-ringing is probably the best way to go, it is a little more expensive, but will save you in the long run. Also head studs will help. A lot of the Euro guys o-ring, the Volvo guys sometimes superglue piano wire to their block to get the effect of o-ringing (withouth the slot of course).

I wish I did it to mine when the engine was out. Right now i am running 15ish psi without problems, adjusted to 18psi yesterday, and was still fine. Backed it down to 15 for now, and probably will back it down to 7-10ish because of gas milage.

Matt has a really nice built up m20.

Re: WHOA!!! 18psi on a M20??? what internal mods????

http://matt325i.home.comcast.net/Webpage/turbo.html

The most important upgrade would probably be the low compression pistons (Ross forged aluminum). Second would be fuel management. These are KEY when you want to boost a lot. If you can fuel it, the power will be crazy.

Re: Very Nice!! What Rods are you using?

Hey,

I am using the stock rods. Have not had any problems with them yet *crosses fingers*.
The turbo is a straight up T04e with a/r ratio's of .50 compressor and .60 turbine. The compressor wheel is 55mm and the exit of the compressor is 2". The turbine has an exit of 2.5". I am not sure what kind of trim it is, or anything like that, there is a tag after Garrett that says G2/84. Not sure what that means (can anyone tell me?).

Be carefull about head bolts

It has been suggested to use industrial bolts, that they are stronger than OEM bolts and ARP studs.

It may be true. But don't forget, a head bolt or stud must have some elasticity in them. I mean, when they are torqued on the head, the steel must be stretched a certain amount to be able to handle the vibrations and keep their torque value.

For example, my ARP studs for my M42 engine are listed in their catalog as "undercut". I didn't know what that meant, but when I received the studs I understood. Let's say that my stud is 12mm diameter. The middle part, between the two threaded ends is machined down to may be 10mm. Why doing that, 12mm is stronger than 10mm, right? Yes but the reason for doing that, is that at 60lb/ft of torque, a 12 mm stud won't stretch, but a 10mm one will. The reason why you want a bolt or stud to stretch (not beyond it's permanent deformation point though, but just a slight %) is to be able to act as a rubber band, and keep everything together during high vibration or heat cycles. A bigger bolt won't do that and may vibrate and get loose.
Well, this is what I understood from the FAQ on ARP web site.